/*
 * Copyright 2017 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.util;

import io.netty.util.internal.ObjectUtil;
import io.netty.util.internal.SystemPropertyUtil;
import java.util.Locale;

/**
 * A utility class for wrapping calls to {@link Runtime}.
 */
public final class NettyRuntime {

  /**
   * Holder class for available processors to enable testing.
   */
  static class AvailableProcessorsHolder {

    private int availableProcessors;

    /**
     * Set the number of available processors.
     *
     * @param availableProcessors the number of available processors
     * @throws IllegalArgumentException if the specified number of available processors is
     * non-positive
     * @throws IllegalStateException if the number of available processors is already configured
     */
    synchronized void setAvailableProcessors(final int availableProcessors) {
      ObjectUtil.checkPositive(availableProcessors, "availableProcessors");
      if (this.availableProcessors != 0) {
        final String message = String.format(
            Locale.ROOT,
            "availableProcessors is already set to [%d], rejecting [%d]",
            this.availableProcessors,
            availableProcessors);
        throw new IllegalStateException(message);
      }
      this.availableProcessors = availableProcessors;
    }

    /**
     * Get the configured number of available processors. The default is {@link
     * Runtime#availableProcessors()}. This can be overridden by setting the system property
     * "io.netty.availableProcessors" or by invoking {@link #setAvailableProcessors(int)} before any
     * calls to this method.
     *
     * @return the configured number of available processors
     */
    @SuppressForbidden(reason = "to obtain default number of available processors")
    synchronized int availableProcessors() {
      if (this.availableProcessors == 0) {
        final int availableProcessors =
            SystemPropertyUtil.getInt(
                "io.netty.availableProcessors",
                Runtime.getRuntime().availableProcessors());
        setAvailableProcessors(availableProcessors);
      }
      return this.availableProcessors;
    }
  }

  private static final AvailableProcessorsHolder holder = new AvailableProcessorsHolder();

  /**
   * Set the number of available processors.
   *
   * @param availableProcessors the number of available processors
   * @throws IllegalArgumentException if the specified number of available processors is
   * non-positive
   * @throws IllegalStateException if the number of available processors is already configured
   */
  @SuppressWarnings("unused,WeakerAccess") // this method is part of the public API
  public static void setAvailableProcessors(final int availableProcessors) {
    holder.setAvailableProcessors(availableProcessors);
  }

  /**
   * Get the configured number of available processors. The default is {@link
   * Runtime#availableProcessors()}. This can be overridden by setting the system property
   * "io.netty.availableProcessors" or by invoking {@link #setAvailableProcessors(int)} before any
   * calls to this method.
   *
   * @return the configured number of available processors
   */
  public static int availableProcessors() {
    return holder.availableProcessors();
  }

  /**
   * No public constructor to prevent instances from being created.
   */
  private NettyRuntime() {
  }
}
